摘要：Aims. Stellar activity is an important source of systematic errors and
uncertainties in the characterization of exoplanets. Most of the techniques used to
correct for this activity focus on an ad hoc data reduction.
Methods. We have developed a software for the combined fit of transits
and stellar activity features in high-precision long-duration photometry. Our aim is to
take advantage of the modelling to derive correct stellar and planetary parameters, even
in the case of strong stellar activity.
Results. We use an analytic approach to model the light curve. The code
KSint, modified by adding the evolution of active regions, is
implemented into our Bayesian modelling package PASTIS. The code is
then applied to the light curve of CoRoT-2. The light curve is divided in segments to
reduce the number of free parameters needed by the fit. We perform a Markov chain Monte
Carlo analysis in two ways. In the first, we perform a global and independent modelling of
each segment of the light curve, transits are not normalized and are fitted together with
the activity features, and occulted features are taken into account during the transit
fit. In the second, we normalize the transits with a model of the non-occulted activity
features, and then we apply a standard transit fit, which does not take the occulted
features into account.
Conclusions. Our model recovers the activity features coverage of the
stellar surface and different rotation periods for different features. We find variations
in the transit parameters of different segments and show that they are likely due to the
division applied to the light curve. Neglecting stellar activity or even only bright spots
while normalizing the transits yields a ~
1.2σ larger and 2.3σ smaller transit depth,
respectively. The stellar density also presents up to 2.5σ differences depending
on the normalization technique. Our analysis confirms the inflated radius of the planet
(1.475 ±
0.031RJ) found by other authors. We show that bright spots
should be taken into account when fitting the transits. If a dominance of dark spots over
bright ones is assumed, and a fit on a lower envelope of the deepest transits is carried
out, overestimating the planet-to-star radius ratio of CoRoT-2 b by almost 3% is likely.
